The well-known varifocal objectives have a pair of axially shiftable components whose displacement with the aid of a camming ring changes the overall focal length from a maximum value in a telephoto position to a minimum value in a wide-angle position. It is also known to design the camming mechanism in such a way that further rotation of the ring beyond the wideangle position will move only one of these shiftable components to displace the previously stationary image plane so as to permit the taking of closeups in the macro range which is usually defined as encompassing image ratios between 1:10 and 1:1.
While it is convenient to have a single control element available for both zooming and closeups, it is frequently desirable to prevent an accidental overshooting of the zoom range when the object or scene to be filmed or photographed is distant from the camera. Furthermore, working near the telephoto end of the zoom range generally requires a steadier support for the camera in order to prevent objectionable blurring, making it desirable to limit the extent of the varifocal adjustment when no tripod or the like is available. It is also known to provide varifocal objectives with diaphragms which automatically increase the relative aperture with changes in the focal length, e.g. from a midposition of the zoom range to the telephoto position. In this case, again, it may be undesirable under certain lighting conditions to move beyond the position where the relative aperture begins to grow larger.
It has already been proposed (see German Pat. No. 1,169,280) to provide a zoom-type camera with a stop which arrests a camming ring in an intermediate position unless the user makes a special effort to deactivate that stop. This mode of operation requires a higher degree of alertness on the part of an operator wishing to utilize the full zoom range.